Technical Field
Embodiments disclosed herein relate generally to the mechanical rotary stabilization of image sensors used for taking photographs or video from an aerial vehicle. While the embodiments disclosed herein may be applicable to a wide range of aircraft, certain embodiments may be particularly applicable to multi-rotor unmanned aerial vehicles (UAVs). Certain embodiments are applicable to a wide range of multi-rotor UAVs, but especially designed for quadrotor UAVs.
Description of the Related Art
UAVs are increasingly being used to capture videos and photographs during flight. When capturing videos or photographs (images) it is desirable that the images are free of any undesired motion. Any rotation of the image sensor creates large changes in what is captured within the field of view of the image sensor, resulting in distorted, shaky and blurred images.
When capturing images from a UAV there are rotational movements of the platform, this case the main body of the UAV, to which the image sensor is attached. The UAV must change its angle to maintain its desired position or flight path; these rotational movements are generally large in amplitude and occur at low frequency. There is also vibration from mechanical and aerodynamic forces on the motors and propellers; these rotational movements are generally small in amplitude and occur at high frequency.
A common solution to this problem is to suspend the image sensor on a gimbal. The gimbal platform to which the image sensor is attached is rotated relative to the outer stages of the gimbal which are attached to the UAV.
Many attempts have been made at building low cost UAV gimbals using servo or brushless motors. The servo driven gimbals are generally very slow and inferior in performance to brushless motor gimbals. Brushless motor gimbals are generally driven by switched transistors to control the torque generated by the motor.
In general a brushless motor gimbal does not have sufficient power to drive the system at high frequencies. It is also challenging to sense small amplitude and high frequency movements because of noise in the sensor. It is thus desired to have a system with a low natural frequency to provide passive isolation of the high frequency disturbances. To achieve a low natural frequency the stiffness of the system must be minimized. Adding mass to the stabilized platform also lowers the natural frequency but is undesirable especially for a UAV where minimizing weight and size is important to safety, flight endurance, and flight performance.